A number of intravascular procedures are currently utilized to treat a stenosis within a body vessel of a human being. A common intravascular procedure is referred to as percutaneous transluminal coronary angioplasty (PTCA or hereinafter “angioplasty”). During a typical angioplasty procedure, a guidewire is initially positioned within the body vessel and a guiding catheter is positioned over the guidewire. Next, a balloon catheter having an inflatable balloon is advanced through the guiding catheter and vessel until the balloon is adjacent to the stenosis. Subsequently, inflation of the balloon compresses the stenosis and dilates the body vessel.
During many diagnostic or interventional catheterization procedures, it is necessary to route the catheter from an entry point, such as either the femoral, brachial or radial artery, to a target location within the vasculature. When properly placing a catheter into position, the catheter should be able to be turned, pulled, and pushed so that the distal end of the catheter can navigate the twists and turns of the blood vessels on its path to the final location. This requires that the catheter be rigid enough to transfer the torque being applied by the operator of the catheter, but also flexible enough so that the catheter will not damage any of the blood vessels of the patient. The catheter can be too stiff, which can prevent the catheter from passing through tortuous blood vessels. Alternately, the catheter can be too soft, which can result in the occurrence of kinks along the length of the catheter. In either of these situations, the usefulness of the catheter in the patient is limited.
In order for intravascular catheters to be neither too stiff nor too soft, it is common to make such catheters with a relatively stiff shaft and a relatively soft distal region. Typically, this variable stiffness is achieved by varying the properties of the materials used to fabricate the catheters. For example, catheters intended for use as angiography catheters or as guiding catheters often comprise a tubular liner surrounded by an outer tubular shell, with a reinforcing layer interposed there between. Either the outer shell or the liner, or both tubular elements may include relatively softer polymeric materials in a distal region of the catheter. Optionally, the reinforcing layer, which is usually a tubular braid, may also have a more flexible, modified form in the distal region.
A problem that has arisen in variable stiffness catheters relates to the challenge of reliable, low-cost manufacturing, especially since many of these devices are discarded after use in only one patient. One fabrication technique taught in the prior art is to make a laminated catheter assembly with uniform polymer materials. Selected regions of the catheter are then modified by radiation treatment to selectively increase stiffness. However, this technique has not become popular due to limitations in the choice of catheter materials and in the control of the final catheter properties. It is therefore more common for intravascular catheters to have a composite construction employing different polymeric materials.
One known technique for manufacturing variable stiffness catheters requires sliding a series of tubular segments having different stiffnesses over an inner assembly comprising a liner surrounded by a reinforcing layer. The tubular segments are shrink-fitted and melt-bonded to the inner assembly using a removable length of heat-shrink tubing. Such a process is tedious and inefficient since catheters can only be fabricated one-at-a-time. In a known reel-to-reel process, outer jacket material is varied by switching between extrusion sources as a length of inner assembly passes through a wire-coating type extruder head. Alternatively, discrete sections of one material are extruded or over-molded onto a length of inner assembly. Then, a different material is extruded onto the length of inner assembly, filling in the spaces between the discrete sections. After forming the continuous, variable-stiffness outer shell, the long assembly is cut into catheter-length sections. Such reel-to-reel processes are more cost-efficient than assembling catheters one-at-a-time. However, the use of different materials to achieve variable catheter stiffness requires multiple assembly steps and/or complex tooling, and the junctions between the different material sections require careful control of design and manufacturing to avoid potentially weak joints that could fail during use.
Accordingly, there is a need for a medical catheter that is simple to manufacture and has varied properties along its length, such as varying catheter stiffness, curve retention, and overall back-up support. The present invention addresses these needs, as well as other problems associated with existing medical catheters. The present invention also offers further advantages over the prior art and solves other problems associated therewith.